Machine tool

ABSTRACT

A machine tool with a vertically reciprocating spindle head has an automatic tool changer including a rotatingly indexable tool support connected to the machine tool frame and vertically movable independently of the spindle head, a first cam-and-crank mechanism activated by spindle head vertical movement to move the tool support with the spindle head during a portion of the tool changing operation, a second cam-and-crank mechanism also activated by spindle head vertical movement for opening and closing a tool holder on the tool support during another portion of the tool changing operation, and a vertical stop for preventing vertical movement of the tool support with the spindle head into the machining region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a machine tool and more particularly to amachine tool equipped with an automatic tool changer (ATC).

2. Description of the prior Art

In a machine tool such as a multi-purpose machining center (MC) forthreading and cutting holes in work pieces, a number of taps and drillsare stored in a redetermined place before machining. Using an ATC, thetool being used can be exchanged with another type tool or a new one,automatically. Various kinds of ATC's have been proposed, and one ATChaving a relatively simple construction has been disclosed in Japanesepatent application Laid-Open No. 58-51046. In that ATC, a disk toolmagazine with many tools radially arranged is rotatably mounted on amain spindle and reciprocates with the main spindle during non-toolchanging machining operations. The tool magazine can slide relative tothe main spindle head only when the main spindle head reaches theautomatic tool changing region which is located directly above itsmachining region, that is, the region wherein the main spindle headnormally moves up and down for machining purposes. In a machine toolwith this type of ATC, the main spindle head first is slid upwardlyrelative to the tool magazine to extract the used tool from the toe ofthe main spindle. Subsequently, the tool magazine is rotatingly indexedto allow a replacement tool to move beneath the main spindle with theirrespective axis aligned. The main spindle then slides downward tocapture the new tool.

Serious disadvantages can exist in a machine tool having an ATC of sucha construction. Because the tool magazine moves together with the mainspindle head during machining operations, tools mounted on the toolmagazine and extending in the radial direction can interfere with thework piece being machined, depending on the shape of the work piece.Another disadvantage is that a machine tool with such an ATC can bequite complicated in construction, be prone to develop trouble, and berelatively expensive.

SUMMARY OF THE INVENTION

The present invention is intended to remedy such shortcomings in machinetools equipped with disk-shaped tool magazines provided with radiallyarranged replacement tools.

It is a specific object of the present invention to provide an ATC witha tool magazine wherein tools extended from the tool magazine do notinterfere with the work piece being machined.

It is another specific object of the present invention to provide atrouble-free inexpensive mechanism for allowing a series of automatictool changing operations to be accomplished, including holding a tool,releasing the tool, extracting the tool from the main spindle, andmounting a newly indexed tool on the main spindle head.

In the machine tool having an ATC according to the present invention, atool support for rotatably supporting a tool magazine is attached to theframe of the machine tool proper. The tool support is movable in theaxial direction independently of the main spindle only above a fixedaxial location, and the tool magazine is made to radially hold a numberof tools in the circumferential direction so as to be able to rotatablyindex a desired tool past a given circumferential position. The indexedtool is arranged to arrive at the toe of the main spindle with its axisformed in line with the axis of the spindle. A first cam-and-crankmechansim in provided to move the tool support together with the mainspindle head vertically over a predetermined distance during "doubleaction" movement of the main spindle head in the automatic tool changingregion, for opening and closing a tool holder attached to the toolmagazine. A second cam-and-crank mechanism cooperates with the mainspindle head to cause a tool holding member installed in the mainspindle to release the tool attached to the toe of the main spindleduring upward movement beyond the predetermined distance, andsubsequently grasp the new or different tool on downward movement of thespindle. In the machine tool thus constructed, the tool magazine beingsupported at the fixed position on the frame does not interfere with awork piece when the main spindle is lowered into the machining region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an arrangement of principalmembers constituting a machine tool embodying the present invention;

FIG. 2 is a vertical section illustrating in detail the internalstructure of the machine tool of FIG. 1;

FIG. 3 is a partially cutaway side view of the machine tool of FIG. 1;

FIG. 4 is a partial top view of FIG. 2 with a partial cross section asan aid for the observation of internal structure;

FIG. 5 is a schematic diagram of the tool magazine used in the FIG. 1embodiment;

FIG. 6 is a schematic diagram of the tool holder used in the FIG. 1embodiment;

FIG. 7(a)-(d) are diagrams illustrating the order of operations of themachine tool of FIG. 1;

FIG. 8 is a schematic diagram of another tool holder made in accordancewith the present invention;

FIG. 9 is a cross sectional view of the tool holder in FIG. 8 taken online IX--IX; and

FIG. 10 is a cross sectional view illustrating a state of operation ofthe machine in FIG. 1 wherein a forked portion provided at the toe of asecond crank is positioned above a pin horizontally projected from themain spindle.

PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the accompanying drawings, preferred embodiments of thepresent invention in the form of a machine tool will now be described indetail. FIG. 1 is a schematic diagram illustrating an arrangement ofprincipal members constituting a machine tool embodying the presentinvention. FIG. 2 is a vertical section illustrating in detail theinternal structure of the machine tool shown in FIG. 1. FIG. 3 is apartially cutaway side view of the machine tool depicted in FIG. 1, andFIG. 4 is a partial top view of FIG. 2 with a partial cross section asan aid for the observation of internal structure.

FIG. 1 is a schematic diagram illustrating the construction of a machinetool 10 embodying the present invention, wherein a main spindle head 18rotatably supporting a main spindle 26 with a tool mount 52 installed atone end, is vertically movably supported by a frame 16 so that a workpiece may be machined as desired. The tool holder 52 is equipped with atool holding member 66 for holding a tool 20, the tool being axiallydetachable therefrom. A tool magazine 22 supplied with a plurality oftool holders 96 radially arranged, is rotatably supported by a toolsupport 24, tool support 24 is supported by a frame 16 for verticallyupward movement independent of the main spindle head 18. There is also afirst cam-and-crank mechanism 162, 28 for causing the tool 20 installedat the toe of the main spindle 26 to be relatively held or released bythe tool holder 96, and a second cam-and-crank mechanism 188, 30 forcausing the tool 20 to be released and pulled out of the main spindle26.

Referring to FIG. 2-7, the principal construction of the machine toolembodying the present invention will now be described in greater detail.As shown in FIGS. 1-4, the rigid frame 16 formed with a box-like hollowcasing, is horizontally fixed to the front face of a column 14 arrangeduprightly on the base 12 of the machine tool 10. The main spindle head18, rotatably supporting the main spindle 26, is vertically movablymounted in the frame 16. As shown in FIGS. 3 and 4, identical guiderails 36, 36' are each perpendicularly fastened respectively via screws34 to each of the perpendicular end faces of a pair of long pillarmembers 32, 32' uprightly arranged and set opposite to each other infront of the column 14. Left and right pairs of slide dowels 38, 38'placed a predetermined space apart in the rear of the main spindle head18 are slidably engaged with the guide rails 36, 36' to ensure thestable vertical elevation of the main spindle head 18.

A support plate 39 is horizontally stretched between the tops of thepair of long pillar members 32, 32' and fixed thereto with bolts. An ACservomotor 40 containing a rotaty encoder 42 is uprightly arranged onthe support plate 39. A ball screw 44 is fastened to the end of thevertical rotary shaft of the servomotor 40 through a coupling 43 and, ascan be appreciated from FIG. 4, the ball screw 44 is perpendicularlydownwardly extended between the pair of guide rails 36, 36'. As shown inFIG. 4, a nut 46 is horizontally fixed through a bolt 48 in the backprojected portion of the main spindle head 18, the ball screw 44 beingpassed through, and engaged with, the nut 46.

When the AC servomotor 40 is activated, the ball screw 44 is rotated inthe predetermined direction to cause linear movement without backlash tothe nut 46, also causing the main spindle head 18 to be perpendicularlyfreely moved relative to the frame to the extent of a predeterminedstroke. That is, the AC servomotor 40, the ball screw 44 and the nut 46engaged therewith constitute a reciprocal driving mechanism for the mainspindle head 18. The vertical stroke of the main spindle head 18, is, asdiscussed later, roughly divided into (1) a machining region A forcausing the work piece to be machined by making a normal repetitivevertical movement and (2) an automatic tool changing region B, which islocated above the region A, for allowing the tool 20 to be attached to,and be detach from, the main spindle 26 through a "double action"operation. See FIG. 3.

During the aforesaid "double action" operation which is carried outwithin the automatic tool changing region, the main spindle headundergoes a single reciprocation wherein a used tool is extracted fromthe spindle and a new or different tool is loaded. As will be more fullydescribed later, there exist three elevational points within toolchanging region B at which specific tool changing actions are initiatedor completed. As a matter of course, the main spindle head 18 shown inFIGS. 1-3 is elevated up to the upper limit of the machining region A(or the lower limit of the automatic tool changing region B) uponcompletion of machining required for the work piece for remains in astandby position until the next machining or tool changing instructionsare given.

As shown in FIG. 2, the hollow cylindrical main spindle 26 is insertedinto a bearing 50 and rotatably supported thereby under the main spindlehead 18. The main spindle 26 has the tool mount 52 at a lower end, andthe upper end is connected to a motor 56 uprightly arranged on top ofthe main spindle head 18 via the output shaft 60 of a reducer 58 througha coupling 54.

As shown in FIG. 2, the tool mount 52 is designed to mount thedetachable tool 20 equipped with an arbor 62 having a tapered shank, bymeans of a conical opening for admitting the arbor 62. A pull stud 64 isprovided at the rear end of the arbor 62 of the tool 20. The tool 20 isattached to the main spindle 26 by engaging the pull stud 64 with thetool holding member 66 which is slidably inserted in the hollow mainspindle 26. The tool holding member 66 is formed with a known collet soarranged as to encircle the neck of the pull stud 64 with a plurality ofballs 68, and to clamp and release the pull stud 64 as the tool holdingmember 66 slides in the hollow portion of the main spindle 26.

As shown in FIG. 2, an annular plug 70 is vertically slidably insertedup to a predetermined height in the hollow of the main spindle 26, andthe upper end of a draw bar 76 is inserted in the vertical hole in theplug 70, fixed thereto, and extends downward along the central axis ofthe main spindle 26. The lower end of the draw bar 76 is connected tothe top of the tool holding member 66. As can be appreciated from FIG.4, oblong slots 74 (only one being shown) opposite to each other aremade in the main spindle at the position of the plug 70 and both ends ofa pin 72 perpendicularly inserted in the plug 70 extend horizontallyoutside the main spindle 26 through the pair of slots 74.

As shown in FIG. 3, a group of compressed conical springs 78 is insertedin between the step formed in the lower hollow portion of the mainspindle and a washer 80 provided at the lower end of the plug 70. Thetool 20 is mounted on the tool mount 52, and the draw bar 76 is locatedin the central portion formed by the group of conical springs 78. Theforce of the conical springs 78 is used to press the plug 70 upward andhold it at the predetermined position, whereupon the tool holding member66 is resiliently drawn up to ensure that it holds the pull stud 64. Afork 81 formed at the tip of a second crank 30 (to be described in moredetail later) is, when in a non-contact state, positioned close to theupper portion of the perpendicular cross pin 72 extending outwardly fromthe main spindle as shown in FIGS. 2, 4 and 10. This arrangement allowsthe draw bar 76 to be lowered by pressing the pin 72 as the crank 30operates. That is, the cooperative operation of the second cam-and-crankmechanism 188, 30 causes the perpendicular cross pin 72 to be forceddownwardly, and the draw bar 76 to be moved accordingly. Draw bar 76, inturn, further lowers the tool holding member 66 and releases the pullstud 64 from the applied pressure derived from the balls 68, therebyreleasing tool 20 from the tool mount 52. The reference character 83 inFIG. 2 designates a cutting tool such as a drill bit or tap detachablyconnected to the tool 20.

The tool support 24 which is supported by the frame 16 in such a mannerthat it is movable in the axial direction independently of the mainspindle 26, will now be described in more detail. In FIG. 4, supportplates 82, 82' are horizontally attached to a pair of opposite sidewalls l6a, l6a' constituting the frame 16. A pair of round guide rail84, 84' are vertically fixed to the tool support 24 (in a manner to bedescribed later), and are slidably inserted in a perpendicularthroughhole suitably made in each of the respective horizontal supportplates 82, 82'. As shown in FIG. 2, a pair of horizontal left and rightsupport plates 86, 86' extend from the lower part of the frame 16, andthe guide rails 84, 84' are slidably inserted in perpendicular holes ineach of the horizontal support plates 86, 86'. The upper and lower endsof each of the guide rails 84, 86' are respectively fixed to a supportplate 91 installed on a top plate 88 horizontally bridged over the topof the tool support 24. A support plate 89 is installed on the bottom ofthe support plate 91.

Accordingly, the tool support 24 can be elevated to certain heights inregion B relative to the frame 16 by sliding the guide rails 84, 84'against the respective pairs of horizontal support plates 82, 86 and82', 86' as the first cam-and-crank mechanism 162, 28 is caused tooperate during the "double action" movement of the main spindle head 18.A stopper bolt 90 is fitted in the support plate 91 installed on top ofthe tool support 24. The height of the stopper bolt 90 is adjustable sothat the tool support 24 can be held at a position having apredetermined height relative to the frame 16 when the bolt is keptstationary in the plane of the horizontal support plate 82.

The tool magazine 22 which holds many tools 20 radially arranged andwhich is capable of rotatingly indexing them, is supported by the toolsupport 24. A supporting shaft 92 having an axis diagonally downwardlyinclined at a predetermined angle relative to the horizontal plane isprojected from, and fixed to, the tool support 24. The tool magazine 22is rotatably supported by the supporting shaft 92 through a bearing 94.As shown in FIGS. 2 and 5, the tool magazine 22 is a disk formed with alarge diameter flat toothed wheel 98 and provided with a plurality ofradially extending tool holders 96 circumferentially arranged on theouter periphery thereof. The large diameter flat wheel 98 is fixed tothe bearing 94 through a bolt 100 and engaged with a pinion 106 fastenedto the rotary shaft 104 of a motor 102. Motor 102, in turn, is fixed tothe tool support 24. The flat wheel 98 is rotated by the motor 102through the pinion 106 to rotate the tool magazine 22 and index arequired tool 20.

As shown in FIG. 2, hollow cylindrical members 108 are arranged insuitable places on tool support 24 so that their axial lines are inparallel with that of the supporting shaft 92. A compressed spring 110resiliently contained in each of the cylindrical members 108 pressindividual balls 112 against the flat wheel 98. On the flat face of thewheel 98 are provided recessed notches 114 at predetermined intervals inthe circumferential direction and, by resiliently seating the balls 112in the notches 114, the tool 20 can be click-stopped in position while adesired tool 20 is indexed.

As shown in FIGS. 2 and 5, a fork member 116 extended in the directionperpendicular to the central axis of the supporting shaft is clamped andfixed to the tip of the supporting shaft 92 through a bolt 118. Asupport plate 120 having a predetermined thickness is bridged over thelower side space between the forked portions of the fork member 116, anda pair of optical sensors comprising light emitting and receivingelements with their optical axes being aligned are oppositely arrangedon a pair of fitting plates 122, 122'. As shown, plates 122, 122' areinstalled in parallel with each other and placed a thickness of thesupport plate 120 apart on the upper and lower faces of the supportplate. A slit disc 126 rotating in combination with the tool magazine22, and being fixed to the bearing 94, is placed in a non-contact statebetween the light emitting and receiving elements. Disc 126 which canpass across the light emitting and receiving elements and selectivelyblock or unblock the light, together with the emitting and receivingelements constitutes an optical senior 124 by which instructions can begiven to an electric control circuit (not shown).

The tool holder 96 arranged on the outer periphery of the tool magazine22 will now be described. The tool holder 96 is, as shown in FIG. 6,composed of a pair of claw members 128, 128' mounted by a finger 130 toenable the claw members to simultaneously open and close. As shown inFIG. 2, a plurality of fingers 130 are fixed by bolts 132 in theperipheral direction of the flat wheel 98 forming the base of the toolmagazine at a predetermined central angle, and extend in the radialdirection. Each finger 130 is formed with a plate member bent at apredetermined angle, and the respective pair of claw members 128, 128'(FIG. 6) bent in a doglegged shape are positioned a predetermined spaceapart on the finger 130 to be rotatable through a predetermined angleabout respective pins 134. A tension spring 136 is resiliently stretchedover both the members. The claw portions of the claw members 128, 128'facing each other are activated by the crank mechanism (in a manner tobe described later) and caused to open and close, whereby a groovedflange 196 formed in the tool 20 can be gripped or released. As shown inFIG. 6, the other ends of the pair of dog-leg-shaped claw members 128,128' are connected via a shaft pin 138, which projects slightly from therear side of the finger 130. When the shaft pin 138 in FIG. 6 is urgedin the Y direction, each of claw members 128, 128' closes and holdsgrooved flange 196 of the tool 20. On the other hand, if the shaft pin138 is urged in the X direction, each of claw members 128, 128' will berotated outwardly, releasing the tool 20 (shown by dashed lines in FIG.6). The angle (relative to wheel 98) of the finger 130, each supportingone of the tool holder 96 on the outer periphery of the tool magazine 22is set in such a manner as to make the axis of the held tool 20 coincidewith the axis of the main spindle 26 when the tool 20 held by the toolholder 96 arrives at the lower side of the tool mount 52 provided at thetoe of the main spindle 26, that is, when wheel 98 is rotatingly indexedabout shaft 92.

The mechanism for opening and closing the tool holder 96 will now bedescribed. As shown in FIG. 2, a crevice 140 is formed en bloc in thelower face portion of the support plate 89 (to the lower end of whichthe guide rail 84 has been fixed) provided in the tool support 24. Abell crank 142 having a desired shape is rotatably pivotally attached toplate 89 at the crevice 140 through a pin 144. A fork 146 is formed inthe lower end of the bell crank 142, with the fork located at theposition where the tool holder 96 arrives at the lower side of the mainspindle 26 after the rotation of the tool magazine 22. The shaft pin 138for selectively driving the claw members 128, 128' to open or close isset in between the legs of the fork 146.

A vertical plate 148 shown in FIGS. 2 and 4 is arranged and fixed to theupper and lower horizontal support plates 82, 86 respectively attachedto the frame 16, and a cam 152 (provided with a bent groove 150 of apredetermined shape) is attached to the front face of the vertical plate148 through a bolt 154. A follower pin 156 is attached to the upper endof the bell crank 142 and is slidably inserted in the bent groove 150 ofthe grooved cam 152. The bell crank 142 pivotally attached to the toolsupport 24 is caused to elevate en bloc when the tool support 24 iselevated by the first cam-and-crank mechanism 162, 28 (to be describedlater). The pin 156 attached to the upper end of the bell crank 142follows the bent groove 150 of the grooved cam 152 fixed to the frame16, and the bell crank 142 turns slightly clockwise around the pin 144.The fork 146 of the bell crank 142 thus drives the shaft pin 138 of thetool holder 96 in the direction of the arrow Y of FIG. 6 to close thepair of the claw members 128, 128'. If the bell crank 142 turnscounterclockwise, the fork 146 drives the shaft pin 138 of the toolholder 96 in the direction of the arrow X and operates to open the pairof claw members 128, 128'.

There will now be described a mechanism for elevating the tool support24 relative to the frame 16 in the automatic tool changing region toachieve the "double action" movement of the main spindle head 18. Asshown in FIGS. 2-4, the first crank 28 (having an L-shape as clearlyshown in FIG. 3) is rotatably pivotally attached to each of the internalfaces of the opposite side walls l6a, l6a' of the frame 16 through ashaft 158. As shown in FIG. 4, the pair of first cranks 28, 28' arearranged in the interior of the side walls l6a, l6a' respectively inopposed relation. Referring to FIG. 3, a roller 160 is rotatablyinstalled at the end of short arm 167 of crank 28. Similar componentsare associated with crank 28' but are not shown in FIG. 3.

With continued reference to FIG. 3, a first plate cam 162 having atilted cam face 164 is attached to the side face of the main spindlehead 18 through a bolt 166. The first plate cam 162 is installed apredetermined space apart from, and under, the roller 160 rotatablyattached to the first crank 28 to locate the main spindle head 18 at theupper limit of the automatic tool changing region B. A contact 170 isfixed to the upper end face of the long arm 168 of first crank 28. Asshown in FIG. 3, contact 170 is slightly separated from the lower end ofthe bolt 172 screwed into the support plate 91 fixed to the top plate 88formed in the tool support 24 en bloc.

Referring again to FIG. 3, when the main spindle head 18 is elevated byturning the servomotor 40 (to be described later), the roller 160 of thefirst crank 28 abuts the tilted cam face of the plate cam 162 attachedto ecch of the side faces of the main spindle head 18 and turns therespective crank 28 clockwise around the axis 158. The contact 170 ofthe long arm 168 then abuts the lower end of the bolt 172 and elevatesthe tool support 22 along the guide rail 84 by the predetermined stroke.The dimensional ratio of the long arm 168 to the short arm 167 of thefirst crank 28 and the bent angle of both arms should be selected suchthat the elevated distance of the main spindle head 18 coincides withthat of the tool support 24 elevated by the first cam-and-crankmechanism 162, 28 and such that their speeds are synchronized with eachother.

A description will now be given of the second cam-and-crank mechanism,which second mechanism operates to make the tool holding member 66provided in the tool mount 22 of the main spindle 26 release the tool 20when the main spindle head 18 and the tool support 24 are moved inanother part of the "double action" motion by the first cam-and-crankmechanism 162, 28. As shown in FIGS. 2 and 4, an L-shaped second crank30 is installed in the main spindle head 18 to be pivotable through apredetermined rotating angle about shaft 176. A roller 180 is rotatablyattached to the toe of the long arm 178 of second crank 30, whereas thetoe of a short arm 182 is, as shown in FIGS. 4 and 10, formed as a fork184. The fork 184 encloses the main spindle, as is positioned slightlyabove the perpendicular cross pin 72 inserted in the plug 70 provided ontop of the draw bar 76. Fork 184 is in a non-contact state when themachine tool is in the tool release instruction receiving mode. Althoughthe main spindle 26 is rotated by the motor 56 during machining, theangular position of the rotary shaft of the motor 56 is controlled toalways stop at a fixed position. Accordingly, the pin 72 which extendsperpendicularly to the main spindle 26 is also caused to stop at thefixed position directly beneath the fork 184 shown in FIG. 4, to ensurethat the fork 184 engages pin 72 when the second crank 30 is operated.

A second plate cam 188 having a cam face with a predeterminedinclination is arranged to cam the second crank 30 during elevationalmovment of the latter component when the main spindle head 18 is furtherelevated in the automatic tool changing region. In the apparatus shownin FIGS. 2 and 4, the second plate cam 188 is fixed to the perpendicularcasing face of the rotary encoder 42 attached to the top of the pillarmember 32 through a bolt 190, and has a tilted cam face 186 orientedperpendicularly downwardly. In operation, as the main spindle head 18 isfurther elevated, the roller 180 rotatably supported at the toe of thelong arm 178 of the second crank 30 will be made to run on the tiltedcam face 186 of the plate cam 188. As a result, the second crank 30 isturned counter-clockwise around the shaft 176 by a predetermined angle.The fork 184 provided at the toe of the short arm 182 contacts theperpendicular cross pin 72 and presses the pin 72 while forcing the drawbar 76 to drop a predetermined distance, thus lowering the tool holdingmember 66. Consequently, the balls attached thereto are released fromthe pull stud 64 and the tool 20 is also released from the tool mount52. A laminated spring 192 is attached to the long arm of the secondcrank 30, and the released end of the laminated spring 192 contacts theupright end face of a horizontal support plate 194 provided on top ofthe main spindle head 18, whereby a clockwise return force is felt onthe crank 30.

The operation of the first cam-and-crank mechanism 162, 28 always occursprior to the operation of the second cam-and-crank mechanism 188, 30. Aswill be described in more detail later, when the main spindle head 18elevated (in this embodiment) a distance of about 20 mm from the basicposition shown in FIG. 2 (i.e., the lower limit position of theautomatic tool changing position B), the first crank 30 is caused tocontact the first plate cam 162 and elevate the tool support 24 acorresponding distance of 20 mm. When the main spindle head 18 iselevated to a distance of 30 mm, the second crank 30 abuts the secondplate cam 188, pushes up the draw bar 76 through the cam action, andreleases the pull stud 64 of the tool 30 from holding the tool holdingmember 66.

FIGS. 8 and 9 show another tool holder 96" attached to the tool magazine22, which tool holder is simpler in construction than that shown in FIG.6, so that the tool is more easily replaceable. The finger 130 arrangedto radially extend at the predetermined central angle in thecircumferential direction of the tool magazine 22 is provided with afixed holding member 200 having an annular opening 198 (partially cutaway) wide enough to axially pass large diameter flange 196 of the tool20". When any particular tool holder 96", selected by indexing the toolmagazine 22, arrives beneath the main spindle head 18, the center of theannular opening 198 is aligned with the axis of the main spindle 26.Three horizontal step through-holes 202 (see FIG. 9) spaced at angles of120° are provided in the annular base of the tool holding member 200,and bar-like projections 204 having spherical ends are inserted in thestep through-holes 202 to protrude from the annular opening 198. Acompressed spring 206 is resiliently inserted in each of thethrough-holes 202 and the force of the spring 206 is made adjustable byturning a screw 208.

As shown in FIG. 9, a crest groove 210 is provided in the periphery ofthe large diameter flange 196 of the tool 20 and, when the tool 20 isinserted in the annular opening 198 of the tool holding member 200, thesemi-spherical ends of the bar-like projections 204 forcefully engagethe crest groove 210 to hold the tool 20. When the main spindle head 18is placed at the fixed position as shown in FIG. 8, the tool 20 mountedon the toe of the main spindle is held by the tool holder 96 through theaforementioned mechanism. Only when the main spindle head 18 is lowered(for a machining operation) below the standby position, the crest groove210 of the flange 196 engaging with the bar-like projection 204 isseparated from the tip thereof and the tool 20 is released.

The operation of the machine tool thus constructed will now bedescribed. In FIG. 2, after the main spindle head 18 completes normalcutting operation, it returns to the standby position in the machiningregion and stops. At this point the main spindle 26 is in a positionwhere the pin 72 crosses the short arm 182 of the second crank 30. Ifthe next instructions are such that the cutting operation should becontinued, the main spindle head 18 will enter the machining region A tomachine the work piece. If, however, the instructions relate to toolchanging, the main spindle head 18 will undergo a "double action"movement and enter the automatic tool changing region B (to be describedlater) Referring now to FIG. 2, because the shaft pin 138 of the toolholder 96 is pressed and held in the direction of X (FIG. 6) by the fork146 of the bell crank 142, the claw members 128, 128' are opened and thetool 20 is released. The crest groove 210 formed in the flange 196 ofthe tool 20 and held by the claw members 128, 128' is located lower thanthe claw members 128, 128' by a distance ("alpha") and, without meansfor compensating for this offset, the tool 20 cannot be held at thefixed position even if both the claw members 128, 128' are closed.However, as the main spindle head 18 is elevated and while it moves tofrom the position in FIG. 2 to that shown in FIG. 7(a), the first platecam 162 moves and covers of distance of until it abuts on the roller 160installed on the first crank 28. This compensates for the crest groove210 being positioned under the claw members 128, 128' by the distance ofα.

When the instructions as to tool changing are given with the machinetool in the state as shown in FIG. 2, the AC servomotor 40 is driven toturn the ball screw 44, and the main spindle head 18 is verticallyelevated up to the automatic tool changing region B. The main spindlehead 18 undergoes the first stage of the "double action" as depicted inFIGS. 7(a) and 7(b). That is, the main spindle head 18 at the positionshown in FIG. 7(a) has been independently elevated by the distance forreasons explained previously. The first plate cam 162 is then caused toabut on the roller 160 of the first crank 28. Then contact 170 installedon the long arm 168 of the crank 28 then engages the lower end of thebolt 172 provided on the support plate 91 of the tool support 24. Atthis time, the AC servomotor 40 is controlled to rotate at a very lowspeed in order to reduce the noise generated by the contact 170 touchingthe bolt 172, after which time the AC motor 20 operates at thepredetermined speed.

As shown in FIG. 7(b), the main spindle head 18 is elevated a distanceof, for instance, 20 mm. During the elevation from FIG. 7(a) to FIG.7(b) the first crank 28 is further turned because of the cam operationassociated with the first plate cam 162 and caused to elevate the toolsupport 24 slidably supported by the frame 16 through the guide rail 84,together with the main spindle head 18, through essentially the samedistance, in this case 20 mm. As the tool support 24 is elevated thebell crank 142 pivotally attached to the upper end thereof follows thebent groove 150 of the groove cam 152. Accordingly, the bell crank 142then drives the shaft pin 138 of the tool holder 96 in the direction ofthe arrow of FIG. 6, closing the pair of claw members 128, 128' to gripflange 196 of the tool 20.

The main spindle head 18 then undergoes the second stage of the "doubleaction" motion to the position shown in FIG. 7(c). During this secondstage, because the roller 160 of the first crank 28 abuts tilted camface 164 of the first plate cam 162, the tool support 24 together withthe main spindle head 18 is elevated a greater distance, for instance,30 mm in this case. As the main spindle head 18 undergoes the secondstage of the "double action" motion, the roller 180 installed on thelong arm 179 of the second crank abuts the second plate cam 188 locatedat the upper fixed position, causing crank 30 to be turnedcounterclockwise around the shaft 176. The fork 184 provided at the endof the short arm 182 then contacts and depresses the perpendicular crosspin 72. As a result, the balls are released from the pull stud 64 of thetool 20, which is also released from the tool mount 56 at the toe of themain spindle 26. As mentioned previously, the tool 20 is still held bythe tool holder 96 installed on the tool magazine and therefore thereleased tool 20 is prevented from dropping. Although the bell crank 142attached to the tool supprt 24 is elevated relative to the groove cam152 fixed to the frame 16, the bell crank does not undergo a cammingoperation because the follower pin 144 has already passed the tiltedportion of the bent groove 150 and is located in the groove portionwhich is in parallel with the axis of the main spindle 26.

The main spindle head 18 subsequently undergoes the third stage of the"double action" motion of the present invention to the position shown inFIG. 7(d). In the third stage, spindle head 18 is elevated a stillgreater distance, for instance, 70 mm in the present case. At this time,because the roller 160 of the first crank 28 engages the flat face ofthe first plate cam 162, no camming action occurs and, accordingly, onlythe main spindle head 18 is allowed to be elevated, and the tool support24 is not elevated. The roller 180 of the second crank 30 runs on theflat face of the plate cam 188, resulting in no camming action of crank30, and the draw bar 76 is kept pressed down to maintain the pull stud64 in a release mode. As mentioned above, because the tool 20 is beingheld at the fixed position by the tool holder 96, the arbor 62 of thetool 20 is pulled out of the tool mount 52 at the toe of the mainspindle 26 as the main spindle head 18 is elevated relative to toolsupport 24. The main spindle head 18 is moved up above the top of thepull stud 64 of the tool 20 held by the tool holder 96 and is stoppedthereat, completing the third stage.

Subsequently, the motor 102 in the tool magazine 22 rotatingly indexesthe extracted tool 20 away from the tool mount, causing a new ordifferent tool 20' to arrive at the position under the tool mount 52 andstop in axial alignment with spindle head 18. Then the above-describedoperations depicted in FIGS. 7(a)-7(d) are repeated, but in reverseorder, to complete the "double action" and to replace the toolautomatically. That is, the main spindle head 18 is lowered by 70 mm andthe arbor 62 of the replacement tool is mounted on the tool mount 52.Spindle head 18 is then further lowered by 30 mm to release the secondcrank 30 from pressing the draw bar 76, whereas the tool holding member66 is caused to engage the pulled stud 64 of the replacement tool underaction of conical springs 78. As the main spindle head 18 and the toolsupport 24 subsequently are lowered by 20 mm, the bell crank 142operates in reverse to press the shaft pin 138 of the tool holder 96 inthe direction of X of FIG. 6 to open the claw members 128, 128', wherebythe replacement tool is released from the tool support 24.

As set forth above, in the machine tool according to the presentinvention, the tool support for rotatably supporting the tool magazineis installed on the frame of the machine tool proper, isolated from themain spindle head but upwardly movable in the axial direction of themain spindle only above a fixed axial location, that is, above the upperlimit of the machinining region A. The tool magazine is so arranged asto be supported at a fixed position on the frame when the main spindleis lowered to machine a work piece in the machining region, so thattools mounted on the magazine can not interfere with the work piece.Moreover, since only vertical motion of the main spindle head in theautomatic tool changing region is required for tool replacement, such amachine tool can be made simple in construction and offer manyadvantages.

What is claimed is:
 1. A machine tool for machining a work piece, themachine tool of the type having as main spindle head rotatablysupporting a main spindle with a tool mount at one end, the spindle headbeing reciprocable relative to the machine tool frame in the axialdirection of the main spindle, the machine tool further comprising:atool holding member installed in the tool mount of said main spindle;automatic means for changing a tool held in said tool holding memberduring "double action" reciprocal tool-changing movement of said spindlehead, said automatic means including: a. a tool support carried on saidframe and movable in the axial direction of said main spindleindependently of said main spindle; b. a tool magazine rotatablysupported on, and axially movable with, said tool support and having aplurality of tool holders each capable of detachably holding said tool,and spaced about the magazine periphery, said magazine for indexing aselected tool holder into and out of axial alignment with said mainspindle; c. first cam-and-crank means interconnecting said main spindlehead, said frame, and said tool support for moving said tool supporttogether with said spindle head a predetermined distance during the"double action" movement of said main spindle head relative to saidframe, the tool being held in said main spindle also being engaged to beheld by one of said plurality of tool holders of the tool magazineduring movement in said predetermined distance; d. second cam-and-crankmeans interconnecting said main spindle head and said frame for causingsaid tool holding member to release the tool from the tool holdingmember during a preselected portion of said "double action" movement;and e. means for preventing movement of said tool support below a fixedaxial location, the spindle head being axially movable below said fixedlocation for performing machining operations.
 2. The machine tool as inclaim 1 wherein said second cam-and-crank means is operative whereversaid spindle head is moved greater than said predetermined distanceduring said "double action" reciprocal movement.
 3. The machine tool asin claim 1 wherein said tool magazine is rotatable about an axis angledwith respect to the axial direction of the main spindle.